The primary aim is to test the hypothesis that the response to a single test dose of the gonadotropin releasing hormone (GnRH) agonist Lupron will distinguish between gonadotropin deficiency (GnD) and constitutional delay of puberty (CDP) better than sleep GnRH (Factrel) tests. The secondary aim is to test the hypothesis that an optimally spaced series of Lupron injections will distinguish hypothalamic from pituitary causes of GnD. Pilot studies will be carried out in normal adult men and women 18-35 years of age. The major test populations will be teenage boys and girls who are normal volunteers or have delayed puberty shown by independent measures to be GnD or CDP.